The instant invention relates generally to a digital impedance measurement system and, in particular, to a digital eddy current proximity system for analyzing and monitoring rotating and reciprocating machinery.
Analog eddy current proximity systems which analyze and monitor rotating and reciprocating machinery are known in the art. These analog systems typically include a proximity probe located proximate a target object (e.g., a rotating shaft of a machine or an outer race of a rolling element bearing) being monitored, an extension cable and analog conditioning circuitry. The target, proximity probe (a noncontacting device which measures displacement motion and position of an observed conductive target material relative to the probe), extension cable and conditioning circuitry components are all designed to interact in such a way that a voltage output from the circuitry is directly proportional to a distance between the probe and the target. This distance is commonly referred to as xe2x80x9cgapxe2x80x9d.
The interaction that takes place between these components is in accord with the following rules: First, the electrical impedance measured at the conditioning circuitry is the electrical combination of the target, the probe including an integral sensing coil and cable, the extension cable and the conditioning circuitry. This impedance is usually called the xe2x80x9cTank Impedancexe2x80x9d or parallel impedance (Zp). Second, this tank impedance is linearized and converted into a voltage directly proportional to gap. Third, the conditioning circuitry measures impedance at a specific frequency that is a function of its own circuitry. Generally, the circuitry runs at the frequency where the reactive component of the tank impedance approaches zero. In other words, the circuitry is a resonant system, so the frequency of operation will be where the phase shift of the impedance is approximately zero degrees. In reality, the phase shift is not exactly zero due to, inter alia, manufacturing and component variations and tolerances of each analog system.
In order to compensate for these variations and tolerances, each analog system is required to be calibrated to have a parallel impedance which is as close as possible to a predefined ideal parallel impedance while remaining substantially unsusceptible to the multitude of variations and tolerances found in the target, probe, extension cable, and conditioning circuitry. Simultaneously, each analog system is calibrated to have a maximum sensitivity to changes in gap. Moreover, each system is generally required to be calibrated to monitor one specific target material.
These analog systems are also generally burdened by temperature variations in the target, the probe including the integral sensing coil and cable, the extension cable and the conditioning circuitry due to the severe temperature variations in rotating and reciprocating machinery environments. Thus, each system is required to be designed around a multitude of component tolerances to compensate for the severe temperature variations engendered in these environments. Furthermore, these analog systems must also be designed around the sensitivity to changes in the conductivity and permeability of the target, the sensing coil, and the cable, which can greatly effect the precision of these systems.
Moreover, interchangeability problems arise from variations in the target, probe, extension cable, and conditioning circuitry which cause the tank impedance (Zp) versus gap to vary slightly from nominal resulting in a proclivity towards, inter alia, variations in incremental scale factor (ISF), variations in average scale factor (ASF) and deviations from a straight line (DSL). The incremental scale factor (ISF), variations in average scale factor (ASF) and deviations from a straight line (DSL) are common ways to specify transducer performance as is well known in the art.
It is critical that the displacement motion or position between the target and the sensing coil of the proximity probe remains within the linear range of the proximity probe for providing accurate and reliable measurements over a wide range of circuit and environmental conditions in order to operate rotating and reciprocating machinery safely and efficiently. Heretofore, the ability to provide accurate and reliable measurements over a wide range of circuit and environmental conditions has been dependent on, inter alia, designing and manufacturing each production unit within close tolerances and going through laborious calibration methods to compensate for the circuit and environmental conditions.
For the foregoing reasons, there is a need for an eddy current transducer system that, inter alia, substantially eliminates the manufacturing and component variations and tolerances of the prior art analog systems, a system that provides correct gap reading for different target materials and a system which is easy to calibrate.
Additionally, there is a need to solve the general problem of compensating for temperature errors, temperature profiles of different target materials and changes in component conductivity and permeability in order to preclude anomalous behavior in eddy current transducer systems.
Furthermore, there is a need for an eddy current transducer system that has better linearity and interchangeability. Moreover, there is a need for an eddy current transducer system that does not require component changes when re-calibrated to a new or different target material.
The instant invention is distinguished over the known prior art in a multiplicity of ways. For one thing, the instant invention provides a unique digital system for digitally measuring an unknown electrical impedance. Additionally, the instant invention provides a digital proximity system that is a direct one for one replacement for existing analog eddy current proximity systems which is compatible with any existing (or future) eddy current proximity probe (a noncontacting device which measures displacement motion and position of an observed conductive or metallic target material relative to the probe) and extension cable assembly. Thus, the instant invention can directly replace the analog conditioning circuitry of prior art analog systems thereby eliminating the anomalies associated with manufacturing and component variations, and tolerances of these systems. Furthermore, the instant invention eliminates the laborious design and calibration methods required to calibrate prior art analog systems in order to compensate for manufacturing and component variations, tolerances and environmental conditions.
In one form, the instant invention provides a system which includes a unique voltage ratio apparatus and method for digitally measuring an unknown electrical component value. The system accomplishes this by digitizing a first voltage impressed across a serial coupling of a first electrical component and a second electrical component, and by digitizing a second voltage impressed across the second electrical component only. Each of the two digitized voltages is then convolved with digitized waveforms to obtain a first and a second complex voltage number. A ratio of the second complex number to a difference between the first and the second complex number is determined and multiplied by a known value of the first electrical component to determine the unknown value of the second electrical component. A resistance means having a known value can be employed as the first electrical component. The second electrical component can take the form of a proximity probe having an unknown impedance value which, when determined by the instant invention, can be correlated to a distance between the probe and a metallic target object being monitored by the probe. Iteratively repeating the voltage ratio method results in continuously digitally determining the unknown impedance values of the probe which can be directly correlated to the continuous displacement motion and position of the target being monitored relative to the probe. In one form, the digitally determined impedance values can be transformed into analog signals and used to trip alarms, circuit breakers, etc., when the signals are outside nominal operating ranges set by plant operators.
Additionally, the instant invention provides a system that can be used as a direct one for one replacement for existing (and future) analog eddy current proximity systems. The system includes a unique apparatus and method for digitally measuring the impedance of a proximity probe and an extension cable (if employed) which includes the unique voltage ratio apparatus and method delineated supra to obtain an unknown impedance of the proximity probe. Then, the system mirrors a circuit equivalent impedance of an existing (or future) analog proximity circuit and combines the measured impedance with the circuit equivalent impedance for defining a parallel or tank impedance. The defined tank impedance is then correlated to a distance between the probe and a metallic target object being monitored by the probe. Hence, the system can continuously digitally determine the unknown impedance value of the probe by iteratively repeating the aforementioned method and then correlate the digitally measured probe impedance values to the continuous displacement motion and position of the target for analyzing and monitoring rotating and reciprocating machinery.
More particularly, the instant invention provides a system which employs at least one eddy current proximity probe having a multi-axial probe cable coupled to a sensing coil located proximate a conductive target to be monitored. The sensing coil is coupled to ground and to a second terminal of a resistor via the probe cable and an extension cable (if employed). A first terminal of the resistor is coupled to a signal generator device that is digitally programmable to generate dynamic driving signals.
The signal generator device can be included in a digital feedback loop which includes means for monitoring the phase of the tank impedance and to provide corrective action (a frequency change) for adjusting that phase. Thus, the signal generator device can be digitally programmed to emulate the operating frequency of any previous (or future) analog proximity system and can also be digitally reprogrammed, in real time, for driving the sensing coil of the probe at one or more frequencies corrective of any anomalous phase shift calculated from the probe or tank impedance or due to any other anomalies within the system. For example, the instant invention can drive the sensing coil at a precise frequency corrective of temperature variations in the probe including the integral sensing coil and probe cable, and in the target.
A filter is interposed between the signal generator device and the first terminal of the resistor to purify the output dynamic signals of the signal generator device by eliminating, inter alia, harmonics that are created in the device. In addition, the filter helps reduce the noise bandwidth of the system which improves a signal to noise ratio. The filtered signal is driven through the resistor, extension cable (if employed), probe cable and coil for inducing eddy currents within the target. In turn, the eddy currents in the target induce a voltage in the sensing coil of the probe and hence, a change in an impedance of the probe and extension cable (if employed) which varies as a function of, inter alia, the displacement motion and position of the target relative to the probe.
The first and second terminals of the resistor are coupled to inputs of a first and a second analog to digital converter respectively. In turn, the outputs of the analog to digital converters are coupled to a digital signal processor including a convolution means. The first analog to digital converter receives and samples a first voltage between the serially coupled resistor, extension cable (if employed), probe cable and coil and outputs a first digital voltage signal to the digital signal processor. The second analog to digital converter receives and samples the voltage between ground and the combination of the extension cable (if employed), the probe cable and the coil and then, outputs a second digitized voltage signal to the digital signal processor. A timing control means is operatively coupled to the analog to digital converters and to the signal generator device such that the sampling is synchronously performed with the driving signal of the signal generator. This ensures, inter alia, that when the voltages are calculated there will be exactly one cycle worth of data stored in each data set.
The digital signal processor convolves the two digitized voltages by convolving each digitized voltage with a digital sine and cosine wave to obtain a first and a second complex voltage number. Once the convolution of the digitized voltages is performed the impedance value of the extension cable (if employed), probe cable and coil can be calculated directly from the measured voltages.
The system includes an open/short/load calibration method which can compensate for cable length included in the second electrical component. For example, the extension cable can be compensated for by using the open/short/load calibration method according to the instant invention. Thus, the system can apply the open/short/load calibration method to the measured impedance to obtain a compensated impedance. Furthermore, the open/short/load calibration method can be utilized to calibrate each printed wire assembly within the system.
The measured impedance or the compensated impedance is then correlated by the system to a gap value by using equations, numerical methods, algorithmic functions or lookup tables wherein gap values are correlated to measured or compensated impedance values defining the gap or spacing interposed between the probe and the target being monitored. This method of measuring gap can be continuously repeated for monitoring, for example the vibration of a rotating shaft of a machine or an outer race of a rolling element bearing.
Additionally, the system can combine the measured impedance or the compensated impedance value with a mathematical model value or an empirically predetermined value of an existing (or future) analog conditioning circuit that is compatible with the particular probe being employed. This value can be called up from a memory means associated with the digital signal processor. The digital signal processor combines this value with the measured impedance or the compensated impedance to obtain a resultant impedance defined as the tank impedance. This tank impedance can be employed to determine the gap between the probe and the target by using equations, numerical methods, algorithmic functions or lookup tables wherein gap values are correlated to tank impedance values. Thus, the existing proximity probe can be retained and this method of measuring gap can be continuously repeated for monitoring, for example the vibration of a rotating shaft of a machine or an outer race of a rolling element bearing that was heretofore monitored by an analog eddy current proximity system.
Gap values can be outputted to a digital to analog converter for providing analog outputs or downloaded to a processing stage for further processing and/or providing digital and/or analog outputs.
The impedance value of analog conditioning circuitry determined from the mathematical model or empirically is typically dependent on operating frequency. Thus, once the tank impedance is determined it can be used to determine if the system is running at the proper frequency. If the system is not running at the proper frequency the digital feedback loop can be used to feedback a signal from the digital signal processor to program the signal generator device for dynamically adjusting the driving signal.
Moreover, the instant invention includes a unique material identification method for automatically identifying a target material and automatically calibrating itself to monitor the identified material thereby eliminating the need for component changes and laborious re-calibration methods inherent with prior art systems. The instant invention also expands the unique material identification method to include a material insensitive method which is capable of outputting a gap value substantially correct for any target material being monitored thereby providing a material insensitive digital proximity system. Thus, the instant invention provides a digital proximity system that does not require component changes when being used to replace an existing system and/or does not require re-calibration when being used with a new or different target material. As a result, the instant invention provides a digital proximity system which can not be mis-calibrated when put into operation and which eliminates the interchangeability problem found in prior art systems.
Additionally, the instant invention includes a unique inductive ratio method which allows a gap versus inductive ratio curve to be determined for a specific target material without knowing the far gap impedance of the probe coil and thus, without removing the probe from a machine being monitored. The gap versus inductive ratio curve determined by this method can be used to determine the gap between the probe and the target being monitored. Furthermore, this method can be used to discern moisture ingress within a probe while it is still in the machine.
Accordingly, a primary object of the instant invention is to provide a new, novel and useful digital eddy current proximity system: apparatus and method.
Another further object of the instant invention is to provide is to provide a new, novel and useful digital system for measuring an unknown electrical value of an electrical component, for example, an unknown impedance value of an electrical component thereby providing a digital impedance measuring device.
Another further object of the instant invention is to provide a digital proximity system as characterized above which includes the digital impedance measuring device employed to measure impedance of an eddy current displacement probe and correlate the measured impedance to a gap between the probe and a target being monitored.
Another further object of the instant invention is to provide a digital proximity system as characterized above which includes means to dynamically measure the impedance of an eddy current probe at bandwidths high enough to support vibration information.
Another further object of the instant invention is to provide a digital proximity system as characterized above which provides a digital proximity system that is compatible with previous (or future) analog eddy current systems and existing signal conditioning sensors including proximity sensors using one or more frequencies.
Another further object of the instant invention is to provide a digital proximity system as characterized above which is capable of emulating the operation of analog conditioning circuitry of eddy current proximity systems for providing backwards (or future) compatibility with analog systems.
Another further object of the instant invention is to provide a digital proximity system as characterized above which includes an open/short/load calibration method which allow various cable length compatibility.
Another further object of the instant invention is to provide a digital proximity system as characterized above which includes a unique automatic material identification and calibration method.
Another further object of the instant invention is to provide a digital proximity system as characterized above which includes a unique material insensitive method.
Another further object of the instant invention is to provide a digital proximity system as characterized above which includes a unique inductive ratio method for measuring gap values.
Another further object of the instant invention is to provide a digital proximity system as characterized above which is self-contained, self-configuring and self-analyzing.
Another further object of the instant invention is to provide a digital proximity system as characterized above which is capable of identifying an eddy current displacement probe that is coupled thereto.
Viewed from a first vantage point, it is an object of the instant invention to provide a device for digitally measuring electrical impedance, comprising in combination: a network including a first electrical component and a second electrical component serially connected; a signal generating means operatively coupled to the network for driving a current through the serially connected components; means for sampling a first voltage impressed across the network and a second voltage impressed across the second component into digitized voltages; means for convolving each the digitized voltage with a digital waveform for forming a first complex number and a second complex number correlative to the first voltage impressed across the network and the second voltage impressed across the second component respectively; means for determining a ratio of the second complex number to a difference between the first and the second complex number, and means for calculating an electrical impedance of the second component by multiplying the ratio by a value of the first component wherein the electrical impedance of the second component is digitally measured.
Viewed from a second vantage point, it is an object of the instant invention to provide a method for digitally measuring electrical impedance, the steps including: forming a network including providing a first electrical component and a second electrical component serially connected; driving the network with a dynamic signal for impressing a voltage across the network and each component; digitizing the voltage across the network and the voltage across the second electrical component; convolving each of the digitized voltages with a digital waveform for forming a first complex number and a second complex number correlative to the voltages across the network and across the second electrical component respectively; determining a ratio of the second complex number to a difference between the first complex number and the second complex number; calculating an electrical impedance of the second electrical component by multiplying the ratio by a know digitized value of the first electrical component wherein the electrical impedance of the second component is digitally measured.
Viewed from a third vantage point, it is an object of the instant invention to provide an apparatus for determining a gap between a proximity probe and a conductive target material, the apparatus comprising in combination: a network including a first electrical component and a proximity probe serially connected; a signal generating means operatively coupled to the network for driving a current through the serial connection wherein a first analog voltage is impressed across the network and a second analog voltage is impressed across the proximity probe; means for sampling and digitizing the first analog voltage impressed across the network and the second analog voltage impressed across the proximity probe into digitized voltages; means for convolving each the digitized voltage with a digital waveform for forming a first complex number and a second complex number correlative to the first analog voltage impressed across the network and the second analog voltage impressed across the proximity probe respectively; means for determining a voltage ratio of the second complex number to a difference between the first complex number and the second complex number; means for processing the voltage ratio into a gap value correlative to a gap between the proximity probe and a conductive target material.
Viewed from a fourth vantage point, it is an object of the instant invention to provide an apparatus for determining a gap between a proximity probe and a conductive target material, the apparatus comprising in combination: a network including an extension cable interposed between and serially connected to a first electrical component and a proximity probe; a signal generating means operatively coupled to the network for driving a current through the serial connection wherein a first analog voltage is impressed across the network and a second analog voltage is impressed across the serial connection of the extension cable and the proximity probe; means for sampling and digitizing the first analog voltage impressed across the network and the second analog voltage impressed across the serial connection of the extension cable and the proximity probe into digitized voltages; means for convolving each the digitized voltage with a digital waveform for forming a first complex number and a second complex number correlative to the first analog voltage impressed across the network and the second analog voltage impressed across the serial connection of the extension cable and the proximity probe respectively; means for determining a voltage ratio of the second complex number to a difference between the first complex number and the second complex number; means for processing the voltage ratio into a gap value correlative to a gap between the proximity probe and a conductive target material.
Viewed from a fifth vantage point, it is an object of the instant invention to provide an apparatus for determining a dynamic gaps between a proximity probe and a conductive target material, the apparatus comprising in combination: means for establishing dynamic voltage signals correlative to dynamic gaps between a proximity probe and a conductive target material; sampling means for digitizing the established dynamic voltage signals into digital voltage signals; a digital multiplier for multiplying each the digital voltage signal by a digital sine signal and a digital cosine signal; means for accumulating values of each multiply in a memory, and means for processing each multiply for obtaining complex voltage representations correlative to dynamic gaps between the proximity probe and a conductive target material.
Viewed from a sixth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the method including the steps of: providing a network of components including a first electrical component and a proximity probe component serially connected; driving a dynamic current through the serially connected electrical components for impressing a first analog voltage across the network and a second analog voltage cross the proximity probe component; sampling and digitizing the first analog voltage impressed across the serially connected resistance and probe components to obtain a first digitized voltage value; sampling and digitizing a second analog voltage impressed across the probe component to obtain a second digitized voltage value; digitally convolving the first digitized voltage and the second digitized voltage into a first complex number and a second complex number respectively; calculating a voltage ratio of the second complex number to a difference between the first complex number and the second complex number; processing the voltage ratio into a gap value correlative to a gap between the proximity probe and a conductive target material.
Viewed from a seventh vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the method including the steps of: providing a network of components including a first electrical component and a proximity probe component serially connected; driving a dynamic current through the serially connected electrical components including the resistance component and the proximity probe component for impressing a first analog voltage across the network and a second analog voltage cross the proximity probe component; sampling and digitizing the first analog voltage impressed across the serially connected resistance and probe components to obtain a first digitized voltage value; sampling and digitizing a second voltage impressed across the probe component to obtain a second digitized voltage value; digitally convolving the first digitized voltage and the second digitized voltage into a first complex number and a second complex number respectively; calculating a voltage ratio of the second complex number to a difference between the first complex number and the second complex number; multiplying the voltage ratio by a value of the first electrical component for determining an impedance of the proximity probe; correlating the determined impedance of the proximity probe to a gap between the proximity probe and a conductive target material.
Viewed from a eighth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the method including the steps of: providing a network of components including a first electrical component, an extension cable component and a proximity probe component respectively serially connected, and locating the proximity probe adjacent a conductive target material; driving a dynamic current through the serially connected electrical components for impressing a first analog voltage across the network and a second analog voltage across the serial connection of the extension cable component and the proximity probe component; sampling and digitizing the first analog voltage impressed across the network to obtain a first digitized voltage value; sampling and digitizing a second analog voltage impressed across the serial connection of the extension cable component and the proximity probe component to obtain a second digitized voltage value; digitally convolving the first digitized voltage value and the second digitized voltage value into a first complex number and a second complex number respectively; calculating a voltage ratio of the second complex number to a difference between the first complex number and the second complex number; processing the voltage ratio into a gap value correlative to a gap between the proximity probe and the conductive target material.
Viewed from a ninth vantage point, it is an object of the instant invention to provide a method for measuring a position of a conductive target material, the steps including: sampling and digitizing a first voltage impressed across a serial connection of a resistance means and a proximity probe located adjacent a conductive target material to obtain a first digitized voltage; sampling and digitizing a second voltage impressed only across the probe to obtain a second digitized voltage, transforming the two digitized voltages into complex voltage numbers; calculating an electrical impedance of the proximity probe by using both complex voltage numbers; correlating the calculated electrical impedance to a gap between the proximity probe and the conductive target material.
Viewed from a tenth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the steps including: sampling and digitizing a first voltage impressed across a serial connection of a first electrical component and a proximity probe located adjacent a conductive target material to obtain a first digitized voltage; sampling and digitizing a second voltage impressed across the probe to obtain a second digitized voltage, transforming the two digitized voltages into complex voltage numbers; determining an electrical impedance of the proximity probe by using both complex voltage numbers; normalizing the electrical impedance of the proximity probe; correlating the normalized electrical impedance of the proximity probe to a gap between the proximity probe and the conductive target material.
Viewed from a eleventh vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the steps including: sampling and digitizing a first voltage impressed across a serial connection of a first electrical component, an extension cable and a proximity probe located adjacent a conductive target material to obtain a first digitized voltage; sampling and digitizing a second voltage impressed across the probe to obtain a second digitized voltage, transforming the two digitized voltages into complex voltage numbers; determining an electrical impedance of the proximity probe by using both complex voltage numbers and compensating for the extension cable; normalizing the electrical impedance of the proximity probe; correlating the normalized electrical impedance of the proximity probe to a gap between the proximity probe and the conductive target material.
Viewed from a twelfth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the method including the steps of: digitally measuring an electrical impedance of a proximity probe located adjacent a conductive target material; combining a predetermined digitized impedance with the digitally measured impedance of the proximity probe; correlating the combined impedance to a gap interposed between the proximity probe and the conductive target material being monitored.
Viewed from a thirteenth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the method including the steps of: digitally measuring an electrical impedance of an a proximity probe and an extension cable connected thereto, the proximity probe is located adjacent a conductive target material; combining a predetermined digitized impedance with the digitally measured impedance; correlating the combined impedance to a gap interposed between the proximity probe and the conductive target material being monitored.
Viewed from a fourteenth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the method including the steps of: measuring an impedance of a proximity probe located proximate a conductive target material and an extension cable operatively coupled to the proximity probe; compensating the measured impedance by using compensation coefficients stored in a memory means; combining a predetermined impedance with the compensated measured impedance for forming a combination impedance; determining a gap between the proximity probe and the conductive target material as a function of the combination impedance; iteratively repeating the measuring, compensating, combining and determining steps to substantially continuously monitor the gap between the probe and the target as a function of the combination impedance.
Viewed from a fifteenth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the steps including: providing a database of normalized impedance curve representations for different conductive target materials; measuring an impedance of a proximity probe located proximate a conductive target material being identified; normalizing the measured probe impedance; utilizing the normalized probe impedance and the database of normalized impedance curve representations for identifying the conductive target material; determining a gap value between the proximity probe and the conductive target material from the normalized probe impedance and the identified target material.
Viewed from a sixteenth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the steps including: providing a representation of a defined series of gap locus each representative of the same gap for different target materials; measuring an impedance of a proximity probe located proximate a conductive target material; normalizing the measured probe impedance; determining a gap value between the proximity probe and the conductive target material from the normalized probe impedance and the representation of the defined series of gap locus wherein the gap value is substantially correct for any conductive target material adjacent the proximity probe thereby providing a material insensitive method for measuring gap values between the proximity probe and different conductive target materials.
Viewed from a seventeenth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the steps including: providing a representation of a defined series of gap locus each representative of the same gap for different target materials; measuring an impedance of a proximity probe located proximate a conductive target material, the proximity probe including a probe cable; compensating an impedance contribution of the probe cable from the measured probe impedance to define a measured coil impedance; normalizing the measured coil impedance; determining a gap value between the proximity probe and the conductive target material from the normalized coil impedance and the representation of the defined series of gap locus wherein the gap value is substantially correct for any conductive target material adjacent the proximity probe thereby providing a material insensitive method for measuring gap values between the proximity probe and different conductive target materials.
Viewed from a eighteenth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the steps including: measuring a proximity probe impedance at a first frequency and a second different frequency, the proximity probe including an integral sensing coil; determining an impedance of the sensing coil from the measured proximity probe impedance at the first frequency and the second different frequency; dividing a reactance of the impedance of the sensing coil at the first frequency by the reactance of the impedance of the sensing coil at the second different frequency for defining an inductive ratio; correlating the inductive ratio to a value representative to a gap between the proximity probe and the conductive target material.
Viewed from a nineteenth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the steps including: sampling and digitizing a first voltage impressed across a serial connection of a resistance means and a proximity probe located adjacent a conductive target material to obtain a first digital voltage correlative to the first voltage at a first frequency; sampling and digitizing a second voltage impressed only across the probe to obtain a second digital voltage correlative to the second voltage at the first frequency, digitally convolving the first digital voltage and the second digital voltage into a first complex voltage number and a second complex voltage number; calculating an electrical impedance of the proximity probe at the first frequency by using the first complex voltage number and the second complex voltage number; sampling and digitizing a third voltage impressed across the serial connection of the resistance means and the proximity probe located adjacent the conductive target material to obtain a third digital voltage correlative to the third voltage at a second frequency; sampling and digitizing a fourth voltage impressed only across the probe to obtain a fourth digital voltage correlative to the fourth voltage at the second frequency, digitally convolving the third digital voltage and the fourth digital voltage into a third complex voltage number and a fourth complex voltage number; calculating a complex electrical impedance of the proximity probe at the second frequency by using the third complex voltage number and the fourth complex voltage number; dividing a reactance of the calculated complex electrical impedance of the sensing coil at the first frequency by the reactance of the calculated complex electrical impedance of the sensing coil at the second different frequency for defining an inductive ratio; correlating the inductive ratio to a value representative to a gap between the proximity probe and the conductive target material.
Viewed from a twentieth vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the steps including: providing a proximity probe having a first end located adjacent a conductive target material and having a second end coupled to a first end of an extension cable; measuring an impedance at a second end of the extension cable; compensating the measured impedance by mathematically eliminating extension cable residuals from the measured impedance for defining a proximity probe impedance of the proximity probe; correlating the proximity probe impedance with a value representative of a gap between the proximity probe and the conductive target material.
Viewed from a twenty-first vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the steps including: providing an extension cable having two ends; determining a first impedance of the extension cable with one of the two ends opened for defining an open impedance; determining a second impedance of the extension cable with one of the two ends shorted for defining a short impedance; providing a proximity probe having an end located adjacent a conductive target material and having an opposite end coupled to one of the two ends of the extension cable; measuring an impedance at the other end of the extension cable; determining an impedance of the proximity probe as a function of the short impedance, the open impedance and the measured impedance for defining a proximity probe impedance; correlating the proximity probe impedance with a value representative of a gap between the proximity probe and the conductive target material.
Viewed from a twenty-second vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the steps including: providing an extension cable having two ends; determining a first impedance of the extension cable with one of the two ends opened for defining a open impedance; determining a second impedance of the extension cable with one of the two ends shorted for defining a short impedance; determining a third impedance of the extension cable with one of the two ends coupled to a load having a known value for defining a load impedance; providing a proximity probe having an end located adjacent a conductive target material and having an opposite end coupled to one of the two ends of the extension cable; measuring an impedance at the other end of the extension cable; determining an impedance of the proximity probe as a function of the short impedance, the open impedance, the load impedance and the measured impedance for defining the proximity probe impedance; correlating the proximity probe impedance with a value representative of a gap between the proximity probe and the conductive target material.
Viewed from a twenty-third vantage point, it is an object of the instant invention to provide a method for measuring a gap between a proximity probe and a conductive target material, the steps including: providing an extension cable having two ends; determining a first load impedance of the extension cable with one of the two ends coupled to a first load; determining a second load impedance of the extension cable with one of the two ends coupled to a second load; the second load having an impedance that is less than the impedance of the first load; providing a proximity probe having an end located adjacent a conductive target material and having an opposite end coupled to one of the two ends of the extension cable; measuring an impedance at the other end of the extension cable; calculating a proximity probe impedance of the proximity probe as a function of the measured impedance, the first load impedance and the second load impedance for compensating for extension cable residuals; correlating the proximity probe impedance with a value representative of a gap between the proximity probe and the conductive target material.
Viewed from a twenty-fourth vantage point, it is an object of the instant invention to provide a method for measuring a characteristic of a conductive target material disposed adjacent a proximity probe, the steps including: providing a length of cable having a first end and a second end; determining a first impedance of the cable with the first end opened for defining a open impedance; determining a second impedance of the cable with the first end shorted for defining a short impedance; coupling the first end of the cable to a proximity probe and having the second end of the cable coupled to a digital eddy current proximity system; measuring, at the second end of the cable, an impedance of the coupled cable and proximity probe; calculating the proximity probe impedance as a function of the measured impedance, the open impedance, and the short impedance for compensating for cable length residuals; correlating the proximity probe impedance with a characteristic of a conductive target material disposed adjacent the proximity probe.
These and other objects and advantages will be made manifest when considering the following detailed specification when taken in conjunction with the appended drawing figures.